Exhaust system for an internal combustion engine of a motor vehicle as well as motor vehicle

ABSTRACT

An exhaust system for an internal combustion engine of a motor vehicle includes an exhaust-gas line and an associated active silencing device. A sound coupling-in line of the silencing device substantially concentrically surrounds the exhaust-gas line on the outside. A first perforation is provided in an axial portion facing away from a sound line in an area of the exhaust-gas line enclosed by the sound coupling-in line. An axial portion facing the sound line is designed perforation-free at least in a portion. Furthermore, a motor vehicle with such an exhaust system is explained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. non-provisional application claiming thebenefit of German Application No. 10 2019 106 159.8, filed on Mar. 11,2019, which is incorporated herein by its entirety.

TECHNICAL FIELD

The disclosure relates to an exhaust system for an internal combustionengine of a motor vehicle, with an exhaust-gas line routing exhaust gasand an active silencing device, wherein the active silencing devicecomprises a sound-generating unit which is acoustically coupled to theexhaust-gas line via a sound line and a sound coupling-in line connecteddownstream thereto, with the result that sound generated by thesound-generating unit can be introduced into an exhaust gas flow presentinside the exhaust-gas line.

Furthermore, the disclosure relates to a motor vehicle with such anexhaust system.

BACKGROUND

Such exhaust systems are known from the state of the art. Via the activesilencing device, sound can be generated which is superposed with asound carried by the exhaust gas flow. Here, the superposition is atleast partly destructive in nature, with the result that the soundcarried by the exhaust gas flow is muffled or cancelled by the activesilencing device.

As a rule, loudspeakers which can function only within a specifictemperature range are used as sound-generating units of such silencingdevices.

In exhaust systems, the situation often arises that a temperature of theexhaust gas flow, which carries the sound to be muffled or cancelled,lies outside the temperature window in which loudspeakers or othersound-generating units function reliably. For this reason, suchcomponents of active silencing devices must be protected against thehigh temperatures of the exhaust gas flow. However, thermal protectionmust not take place at the expense of the acoustic effectiveness of thesilencing device. In other words, in exhaust systems with activesilencing devices, a compromise between acoustic effectiveness andreliability must always be chosen.

An exhaust system is to be provided that has an active silencing device,which is acoustically particularly effective and at the same timefunctions reliably. In particular, the active silencing device is to bereliably protected against the thermal influences of the exhaust gasflow.

SUMMARY

An exhaust system has a sound coupling-in line that substantiallyconcentrically surrounds an exhaust-gas line on an outside, and an areaof the exhaust-gas line enclosed by the sound coupling-in line has anaxial portion facing a sound line and an axial portion connecteddownstream thereto facing away from the sound line. A first perforationis provided in the axial portion facing away from the sound line and theaxial portion facing the sound line is designed perforation-free atleast in a portion. A sound generated by the sound-generating unittherefore firstly runs through the sound line and thus passes into thesound coupling-in line, to be more precise into an annular space betweenthe sound coupling-in line and the exhaust-gas line. From here, thesound passes into the inside of the exhaust-gas line via the firstperforation and can thus interact with the sound carried by the exhaustgas flow. By a perforation is meant in this connection a group ofopenings which are arranged with a degree of regularity. An axialportion designed perforation-free at least in a portion is here eitherdesigned wholly without perforation or has a perforation merely in oneportion. Compared with the axial portion facing away from the soundline, the portion facing the sound line is thus less markedlyperforated. This can be effected, for example, in that a total crosssection of the perforation openings in the axial portion facing thesound line is lower than a total cross section of the perforationopenings in the axial portion facing away from the sound line. Becausethe axial portion facing the sound line is designed perforation-free atleast in a portion, i.e. has no openings at least in a portion, a flow,coming from this axial portion, of a possibly hot exhaust gas flow intothe sound line is reduced or wholly prevented. Consequently, a flow ofhot exhaust gas to the sound-generating unit is thus also reduced orprevented. A flow of hot exhaust gas in the direction of thesound-generating unit can thus substantially only take place via theaxial portion facing away from the sound line and the first perforationprovided there. The sound-generating unit is thus protected against adirect inflow by a hot exhaust gas flow because such an inflow is whollyor partly prevented. An exhaust gas flow exiting the exhaust-gas linevia the first perforation can reach the sound-generating unit only viaseveral deviations. This means that the exhaust gas flow coolssignificantly on its way to the sound-generating unit. Thus, thesound-generating unit is effectively protected against the temperatureinfluences of the exhaust gas flow. As a result, it functions reliablyand is durable. At the same time, the sound-generating unit can bearranged relatively close to the exhaust-gas line, as a result of whichthe latter can be operated efficiently and effectively from an acousticpoint of view. Moreover, an exhaust system designed in this way can beconstructed comparatively compact. In other words, it requires only acomparatively small installation space on a motor vehicle which isfitted with such an exhaust system. It can also be flexibly integratedinto available installation spaces.

The idea underlying the disclosure is to perforate that area of theexhaust-gas line which is surrounded by the sound coupling-in line butlies in the region of the sound line as little as possible or not atall. The region of the sound line is to be understood as an axialportion of the exhaust-gas line which lies opposite a mouth of the soundline into the sound coupling-in line. The perforation, which isnecessary for the acoustic coupling of the sound-generating unit to theinside of the exhaust-gas line, is arranged as far as possible outsidethe abovementioned region, thus in an axial portion of the exhaust-gasline facing away from the sound line. Here, the axial portion facingaway from the sound line can directly adjoin the portion, facing thesound line, that is perforation-free at least in a portion or bearranged at a particular distance from the portion that isperforation-free at least in a portion.

Consequently, such an exhaust system is close to ideal in that thesound-generating unit is coupled resistance-free from an acoustic pointof view to the inside of the exhaust-gas line, but at the same timeexhaust gas cannot flow out of the inside of the exhaust-gas line to thesound-generating unit.

A further thermal decoupling of the sound-generating device from theexhaust gas flow can be achieved by lengthening the sound line. Thegeometric distance of the sound-generating unit from the exhaust-gasline is thereby increased.

The first perforation advantageously runs around the whole periphery ofthe axial portion of the exhaust-gas line facing away from the soundline. This results in an effective coupling of the sound generated bythe sound-generating unit into the inside of the exhaust-gas line.

The openings comprised by the first perforation preferably each have asubstantially round cross section. It has become apparent that such afirst perforation is particularly suitable for coupling the activesilencing unit to the inside of the exhaust-gas line and at the sametime limiting an outflow of exhaust gas via the first perforation.

In an embodiment, the exhaust-gas line has a second perforation in thearea enclosed by the sound coupling-in line upstream of the firstperforation in a peripheral portion facing away from the sound line,wherein a peripheral portion facing the sound line is designedperforation-free. The peripheral portion facing away from the sound lineand the peripheral portion facing the sound line are preferablycomplementary to each other to form the whole periphery of theexhaust-gas line, i.e. there are no further peripheral portions. Thissecond perforation serves to acoustically couple the sound-generatingunit to the inside of the exhaust-gas line. A sound generated by thesound-generating unit therefore firstly runs through the sound line andthus passes into the sound coupling-in line, to be more precise into anannular space between the sound coupling-in line and the exhaust-gasline. From here, the sound passes into the inside of the exhaust-gasline via the second perforation and can thus interact with the soundcarried by the exhaust gas flow. By a perforation is again meant a groupof openings which are arranged with a degree of regularity. Because theperipheral portion facing the sound line is designed perforation-free,thus has no openings, a possibly hot exhaust gas flow coming from theinside of the exhaust-gas line is prevented from flowing directly intothe sound line and in this way reaching the sound-generating unit. Aflow of hot exhaust gas in the direction of the sound-generating unit isinstead possible only via the peripheral portion facing away from thesound line and the second perforation provided there. Thesound-generating unit is thus protected against a direct inflow by a hotexhaust gas flow. An exhaust gas flow exiting the exhaust-gas line viathe second perforation can reach the sound-generating unit only viaseveral deviations. This means that the exhaust gas flow coolssignificantly on its way to the sound-generating unit. Thus, thesound-generating unit is particularly effectively protected against thetemperature influences of the exhaust gas flow. Moreover, an exhaustsystem designed in this way can be constructed comparatively compact.

For the case where both a first and a second perforation are provided,it can happen that exhaust gases exit the inside of the exhaust-gas linevia the second perforation. They can then be returned into theexhaust-gas line again via the first perforation. This is possible dueto the downstream arrangement of the first perforation relative to thesecond perforation. The static pressure prevailing within theexhaust-gas line namely decreases along the flow direction of theexhaust gas. An exhaust gas flow which has exited the exhaust-gas linevia the second perforation at comparatively high pressure can thusre-enter the inside of the exhaust-gas line along the pressure gradientvia the first perforation. The pressure ratios are reversed in the gapbetween the exhaust-gas line and the sound coupling-in line. Here, thehighest static pressure is reached at the downstream end of the gap,thus in the area of the first perforation. Because of these pressureratios, hot exhaust gases are consequently prevented from flowing in thedirection of the active silencing unit.

A radial rib, which preferably extends up to the sound coupling-in line,can be provided on an outer surface of the exhaust-gas line between theperipheral portion facing away from the sound line and the peripheralportion facing the sound line. Such a radial rib represents a flowobstacle for an exhaust gas flow which flows out of the inside of theexhaust-gas line in the direction of the sound-generating unit. Thus,the inflow of hot exhaust gas into the active silencing device isfurther prevented. In addition, the radial rib can be formed as coolingfin for the exhaust-gas line. Thus, the exhaust gas flow present insidethe exhaust-gas line is cooled by via the radial rib.

The radial rib can either be attached to the exhaust-gas line on theoutside and extend in the direction of the sound coupling-in line or beattached to the sound coupling-in line on the inside and extend in thedirection of the exhaust-gas line. It is likewise possible for theradial rib to be connected both to the outside of the exhaust-gas lineand to the inside of the sound coupling-in line. For example, the radialrib can be welded to the exhaust-gas line and/or the sound coupling-inline. It is likewise possible to manufacture the radial rib integralwith the exhaust-gas line and/or the sound coupling-in line.

According to an embodiment, a radial rib is provided in each of the twoborder areas between the peripheral portion facing away from the soundline and the peripheral portion facing the sound line. Thus, a total oftwo radial ribs are provided. They each represent a flow obstacle at thetransition point between the peripheral portion facing away from thesound line and the peripheral portion facing the sound line, with theresult that, as already described above, the inflow of hot exhaust gasinto the sound line is impeded or prevented. The two radial ribs arearranged, for example, radially opposite, thus they are offset relativeto each other by an angle of 180° on the periphery of the exhaust-gasline. Naturally, it is also possible to choose a different angle here.Thus, for example, the peripheral portion facing away from the soundline can merely cover an angle of 90° and the peripheral portion facingthe sound line can cover an angle of 270°. Intermediate values are alsopossible. As a result of the second radial rib, the protection of theactive silencing unit against hot exhaust gases is particularlyeffective.

The radial rib is preferably shorter in axial direction of theexhaust-gas line than the sound coupling-in line. Thus, at an axial endof the annular space formed by the exhaust-gas line and the soundcoupling-in line, an acoustic coupling channel results via which soundgenerated by the sound-generating unit can flow around the radial rib orthe radial ribs on the periphery of the exhaust-gas line. Only as itprogresses further can the sound pass into the inside of the exhaust-gasline via the second perforation. An effective acoustic coupling of thesilencing device to the inside of the exhaust-gas line is therebyguaranteed.

An exhaust system in which the radial ribs merely extend to an axiallength which corresponds to the axial length of the second perforationis particularly preferred. Thus, no radial ribs are provided in the areaof the first perforation.

In a variant, the openings comprised by the second perforation each havea substantially rectangular cross section, wherein preferably a shortside of the rectangle is oriented in peripheral direction and a longside of the rectangle is oriented in axial direction of the exhaust-gasline. It has become apparent that a second perforation designed in sucha way effects a good compromise between a thermal decoupling of theinside of the exhaust-gas line from the active silencing device and aneffective acoustic coupling of these components.

An alternative design provides that a radial outer end of the radial ribor radial ribs provided on the outer surface of the exhaust-gas line isor are at a radial distance from the sound coupling-in line, whereineach radial rib radiating from the exhaust-gas line is complemented by aradial rib, pointing radially inwards radiating from the soundcoupling-in line, which is at only a small peripheral distance from theassociated radial rib radiating from the exhaust-gas line or touches theperiphery of same, and the radial inside end of which is at a radialdistance from the exhaust-gas line. Each radial rib provided on theouter surface of the exhaust-gas line forms a so-called radial rib pairtogether with the radial rib allocated to it provided on the soundcoupling-in line. An alternative term for this is double rib. Such aradial rib pair represents an effective flow obstacle for hot exhaustgases, with the result that the active sound-generating unit isprotected against high temperatures. The fact that the radial ribradiating from the outer surface of the exhaust-gas line is notconnected to the sound coupling-in line and the radial rib radiatingfrom the sound coupling-in line is not connected to the exhaust-gas lineis advantageous in terms of production technology. Namely, the necessityof attaching a radial rib both to the exhaust-gas line and to the soundcoupling-in line, which is complex, is avoided. Moreover, the omissionof such connections results in a particularly long service life of theexhaust system as the connection points are often exposed tocomparatively high stresses.

The small peripheral distance between the radial ribs forming the radialrib pair is to be seen in comparison with the line diameter of theexhaust-gas line and means that the distance is at most 10%, preferablyat most 5%, of the line diameter. In this way, it is achieved that hotexhaust gas, given a flow in the direction of the active silencingdevice, is effectively countered by a flow resistance.

In an area upstream of the sound coupling-in line, the exhaust-gas linecan have an axial bend or an axial kink, in particular wherein an axialbend of substantially 90° is present. The sound coupling-in line ispreferably arranged directly adjacent to the axial bend or the axialkink. A compact construction of the exhaust system thus results. As aresult of an axial kink or an axial bend, the pressure ratios inside theexhaust-gas line can be influenced in a targeted manner in an areadownstream of the axial kink or of the axial bend. In particular, apressure level is thereby increased in a convex area of the axial bendor of the axial kink. The pressure level decreases correspondingly in aconcave area.

In this case, the second perforation is preferably arranged downstreamof a convex area of the axial bend or of the axial kink. As alreadyexplained, the second perforation is arranged in a peripheral portionfacing away from the sound line. Because the axial bend or the axialkink causes the pressure in the exhaust gas flow to be higher on theconvex side than on the concave side, an exhaust gas flow in thedirection of the sound-generating unit is thus effectively prevented.

A center axis of the sound line can run substantially along a radialdirection of the sound coupling-in line. By this is meant that apredominant proportion of the direction of the center axis of the soundline is oriented in radial direction of the sound coupling-in line. Asmaller proportion can also run in axial direction and/or in peripheraldirection of the sound coupling-in line. The center axis of the soundline can thus impinge obliquely on the sound coupling-in line, whereinthe radial component is always the largest. However, it is preferredthat the sound line runs along the radial direction of the soundcoupling-in line. This effects a high-quality acoustic coupling of thesound-generating unit to the inside of the exhaust-gas line. Moreover, acompact construction of the exhaust system can thus be achieved.

In addition, a motor vehicle of the type mentioned at the beginning isprovided which comprises an exhaust system according to the disclosure.Such a motor vehicle emits only little or no sound at all via an exhaustgas flow conducted into the surroundings by the exhaust system. Thus,the motor vehicle can be operated comparatively quietly. At the sametime, the motor vehicle is particularly reliable and durable because thetemperature-sensitive components of the exhaust system are protectedagainst hot exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is explained below with reference to various embodimentexamples which are shown in the attached drawings. There are shown in:

FIG. 1 shows a schematic view of a motor vehicle according to thedisclosure with an exhaust system according to the disclosure,

FIG. 2 shows the exhaust system according to the disclosure in a viewfrom above,

FIG. 3 shows a perspective view of the exhaust system from FIG. 2,wherein a sound line and a sound coupling-in line are representedtransparent,

FIG. 4 shows the exhaust system from FIG. 2 in a view from above,wherein the sound line and the sound coupling-in line are omitted,

FIG. 5 shows a perspective view of the exhaust system from FIG. 2,wherein, as in FIG. 4, the sound line and the sound coupling-in line areomitted,

FIG. 6 shows a schematic detail view of a radial rib of the exhaustsystem from FIG. 2,

FIG. 7 shows a schematic detail view of a radial rib of the exhaustsystem from FIG. 2 according to an alternative design and

FIG. 8 shows a schematic detail view of a radial rib of the exhaustsystem from FIG. 2 according to a further alternative design.

DETAILED DESCRIPTION

FIG. 1 shows a motor vehicle 10 with an internal combustion engine 12which is coupled to an exhaust system 14. Thus, the exhaust gas producedby the internal combustion engine 12 is conducted into the surroundings16 via the exhaust system 14.

The exhaust system comprises an exhaust-gas line 18 routing the exhaustgas and an active silencing device 20.

The active silencing device 20 has a sound-generating unit 22 whichcomprises, for example, a loudspeaker and a sound line 24. A soundcoupling-in line 26 is connected to the sound line 24 downstream.

A center axis of the sound line 24 runs substantially along a radialdirection of the sound coupling-in line 26. The center axes of the soundline 24 and the sound coupling-in line 26 are thus substantiallyperpendicular to each other.

Furthermore, the sound coupling-in line 26 surrounds the exhaust-gasline 18 substantially concentrically on the outside. The center axes ofthe sound coupling-in line 26 and the exhaust-gas line 18 are thussubstantially coincident.

The active silencing device 20, more precisely the sound-generating unit22, is acoustically coupled to an exhaust gas flow present inside theexhaust-gas line 18. Here, sound generated by the sound-generating unit22 is conducted into the sound coupling-in line 26 via the sound line 24and thus passes into an annular space which is formed by the soundcoupling-in line 26 and the exhaust-gas line 18.

The portion of the exhaust-gas line 18 running inside this annular spacecan be subdivided into an axial portion facing the sound line 24 and anaxial portion, connected downstream thereto, facing away from the soundline 24.

In the embodiment represented, the axial portion facing the sound line24 and the axial portion facing away from the sound line 24 are directlyadjacent to each other.

Here, a first perforation 38 is provided in the axial portion facingaway from the sound line 24. The axial portion facing the sound line 24is designed perforation-free in a portion, as will be explained later.

The first perforation 38 runs around the whole periphery of the axialportion facing away from the sound line 24.

Here, the openings of the first perforation 38 have a substantiallyround cross section. Within the axial portion facing the sound line 24,the exhaust-gas line 18 furthermore comprises a peripheral portion 28 afacing the sound line 24 and a peripheral portion 28 b facing away fromthe sound line 24. In the embodiment example represented, the twoperipheral portions 28 a, 28 b are complementary to each other to formthe whole periphery of the exhaust-gas line 18.

A second perforation 30 is provided in the peripheral portion 28 bfacing away from the sound line 24. The peripheral portion 28 a facingthe sound line 24 is designed perforation-free.

The sound generated by the sound-generating unit 22 which has alreadyreached the abovementioned annular space, can thus interact with theexhaust gas flow present inside the exhaust-gas line 18 via the firstperforation 38 and/or the second perforation 30.

Here, the openings comprised by the second perforation 30 each have asubstantially rectangular cross section, wherein the short sides of therectangle are each oriented in peripheral direction and the long sidesof the rectangle are each oriented in axial direction of the exhaust-gasline 18.

Furthermore, the exhaust-gas line 18 has an axial bend 32 in an areaupstream of the sound coupling-in line 26 which is designed as a 90°bend in the embodiment example represented.

The second perforation 30 and the axial bend 32 are arranged relative toeach other such that the second perforation 30 is positioned downstreamof a convex area of the axial bend 32.

Moreover, the exhaust system 14 represented comprises a radial rib 34 ineach of the border areas between the peripheral portion 28 b facing awayfrom the sound line 24 and the peripheral portion 28 a facing the soundline 24.

These can be designed in different ways.

In the variant according to FIG. 6, the radial rib 34 is attached to aninner surface of the sound coupling-in line 26 and extends in thedirection of the exhaust-gas line 18. Here, a radial distance 36 can beprovided between the end of the radial rib 34 lying inside and theexhaust-gas line 18. Equally, the radial rib 34 can touch theexhaust-gas line 18 or be connected thereto.

Alternatively, according to FIG. 7, the radial rib 34 can be attached tothe exhaust-gas line 18 and extend in the direction of the soundcoupling-in line 26. A radial distance 36 can again be provided whichresults between the outer end of the radial rib 34 and the soundcoupling-in line 26. It is equally conceivable that the radial rib 34touches the sound coupling-in line 26 with its outer end or is connectedto same.

Instead of a single radial rib 34 in each border area between theperipheral portion 28 a facing the sound line 24 and the peripheralportion 28 b facing away from the sound line 24, a radial rib pair canalso be provided which comprises radial ribs 34 a, 34 b. In thisconnection, the radial rib 34 a is attached to the sound coupling-inline 26 and extends in the direction of the exhaust-gas line 18. Incontrast, the radial rib 34 b is attached to the exhaust-gas line 18 andextends in the direction of the sound coupling-in line 26.

In peripheral direction, the radial ribs 34 a, 34 b are only slightlyspaced apart from each other or touch each other.

In radial direction, the radial rib 34 a radiating from the soundcoupling-in line 26 has a radial distance 36 a from the exhaust-gas line18 at its inner end. The radial rib 34 b radiating from the exhaust-gasline 18 leaves a radial distance 36 b free between its outer end and thesound coupling-in line 26.

In all variants, the radial ribs 34, 34 a, 34 b are shorter in an axialdirection of the exhaust-gas line 18 and of the sound coupling-in line26 arranged concentric thereto than the sound coupling-in line 26. Thus,there is an axial portion of the sound coupling-in line 26 in whichthere can be flow around the radial ribs 34, 34 a, 34 b in peripheraldirection of the exhaust-gas line 18. To be more precise, the radialribs 34, 34 a, 34 b extend merely in the area of the second perforation30.

The mode of operation of the exhaust system 14 is as follows.

The sound generated by the sound-generating unit 22 flows via the soundline 24 into the sound coupling-in line 26. There, it enters into theinside of the exhaust-gas line 18 via the openings of the firstperforation 38. Furthermore, after the sound has flowed around theradial ribs 34, 34 a, 34 b in the area of the first perforation 38, italso passes into the inside of the exhaust-gas line 18 via the openingsof the second perforation 30. In this way, a sound carried by theexhaust gas flow inside the exhaust-gas line 18 is actively muffled.

However, hot exhaust gas can also flow via the openings of the firstperforation 38 and the second perforation 30 from the inside of theexhaust-gas line 18 into the annular space formed by the exhaust-gasline 18 and the sound coupling-in line 26. The active silencing device20 and in particular the sound-generating unit 22 are to be protectedagainst these hot exhaust gases.

Exhaust gas exiting via the openings of the second perforation 30 mustfirst flow around the radial ribs 34, 34 a, 34 b on its path in thedirection of the sound-generating unit 22. Here, the radial ribs 34, 34a, 34 b represent a flow obstacle on the one hand and cool the exhaustgas on the other.

In addition, because of the flow ratios inside the exhaust-gas line 18,a large part of the exhaust gas which has exited via the openings of thesecond perforation 30 is conducted back inside the exhaust-gas line 18via the openings of the first perforation 38. This is due to the factthat inside the exhaust-gas line 18 a higher pressure prevails in thearea of the second perforation 30 than in the area of the firstperforation 38. In the annular space, the pressure ratios are reversed,with the result that a higher static pressure prevails in the area ofthe first perforation 38. This also serves to protect thesound-generating unit 22 against high temperatures.

A direct flow of hot exhaust gas into the sound-generating unit 22 isalso prevented in that the peripheral portion 28 a facing the sound line24 is designed perforation-free.

Although various embodiments have been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this disclosure. For that reason, the followingclaims should be studied to determine the true scope and content of thisdisclosure.

1. An exhaust system for an internal combustion engine of a motorvehicle comprising: an exhaust-gas line routing exhaust gas; an activesilencing device that comprises a sound-generating unit which isacoustically coupled to the exhaust-gas line via a sound line and asound coupling-in line connected downstream thereto, such that soundgenerated by the sound-generating unit can be introduced into an exhaustgas flow present inside the exhaust-gas line; wherein the soundcoupling-in line substantially concentrically surrounds the exhaust-gasline on an outside and an area of the exhaust-gas line enclosed by thesound coupling-in line has an axial portion facing the sound line and anaxial portion connected downstream thereto facing away from the soundline; and wherein a first perforation is provided in the axial portionfacing away from the sound line and the axial portion facing the soundline is designed perforation-free at least in a portion.
 2. The exhaustsystem of claim 1 wherein the first perforation runs around a wholeperiphery of the axial portion of the exhaust-gas line facing away fromthe sound line.
 3. The exhaust system of claim 1 wherein openingscomprised by the first perforation each have a substantially round crosssection.
 4. The exhaust system of claim 1 wherein, in the area enclosedby the sound coupling-in line upstream of the first perforation, theexhaust-gas line has a second perforation in a peripheral portion facingaway from the sound line, wherein a peripheral portion facing the soundline is designed perforation-free.
 5. The exhaust system of claim 4wherein at least one radial rib is provided on an outer surface of theexhaust-gas line between the peripheral portion facing away from thesound line and the peripheral portion facing the sound line.
 6. Theexhaust system of claim 4 wherein at least one radial rib is provided onan inner surface of the sound coupling-in line between the peripheralportion facing away from the sound line and the peripheral portionfacing the sound line.
 7. The exhaust system of claim 5 wherein the atleast one radial rib comprises a plurality of ribs with one radial ribbeing provided in each of two border areas between the peripheralportion facing away from the sound line and the peripheral portionfacing the sound line.
 8. The exhaust system of claim 5 wherein the atleast one radial rib is shorter in an axial direction of the exhaust-gasline than the sound coupling-in line.
 9. The exhaust system of claim 4wherein openings comprised by the second perforation each have asubstantially rectangular cross section.
 10. The exhaust system of claim5 wherein a radial outer end of the at least one radial rib or radialribs provided on the outer surface of the exhaust-gas line is or are ata radial distance from the sound coupling-in line, wherein each radialrib radiating from the exhaust-gas line is complemented by a radial rib,pointing radially inwards radiating from the sound coupling-in line,which is at only a small peripheral distance from an associated radialrib radiating from the exhaust-gas line or touches the periphery ofsame, and the radial inside end of which is at a radial distance fromthe exhaust-gas line.
 11. The exhaust system of claim 1 wherein, in anarea upstream of the sound coupling-in line, the exhaust-gas line has anaxial bend or an axial kink.
 12. The exhaust system of claim 11 wherein,in the area enclosed by the sound coupling-in line upstream of the firstperforation, the exhaust-gas line has a second perforation in aperipheral portion facing away from the sound line, wherein a peripheralportion facing the sound line is designed perforation-free, and whereinthe second perforation is arranged downstream of a convex area of theaxial bend or of the axial kink.
 13. The exhaust system of claim 1wherein a center axis of the sound line runs substantially along aradial direction of the sound coupling-in line.
 14. The exhaust systemof claim 5 wherein the at least one radial rib extends up to the soundcoupling-in line.
 15. The exhaust system of claim 6 wherein the at leastone radial rib extends up to the sound coupling-in line.
 16. The exhaustsystem of claim 9 wherein a short side of the rectangle is oriented in aperipheral direction and a long side of the rectangle is oriented in anaxial direction of the exhaust-gas line.
 17. The exhaust system of claim11 wherein the axial bend or axial kink is substantially 90°.
 18. Amotor vehicle with an exhaust system of claim 1.